Vapor generating, superheating and reheating unit



June 23, 1959 W. H. R OWAND ETAL Filed May 10, 1955 FIG WILL H. ROWANDCHARLES L. MARQUEZ BY CLYDE B. BAVER ARTHUR J. HUGHES TTORNEY UnitedStates Patent F VAPOR GENERATING, SUPERHEATING AND REHEATING UNIT WillH. Rowand, Short Hills, Charles L. Marquez, Jersey City, Clyde B. Bayer,Fanwood, and Arthur J. Hughes, Packanack Lake, N.J., assignors to TheBabcock 8: Wilcox Company, New York, N.Y., a corporation of New JerseyApplication May 10, 1955, Serial No. 507,346

9 Claims. (Cl. 122-481) This invention relates toa high capacity andhigh pressure vapor generating unit having therein a high temperaturevapor superheater and a high temperature vapor reheater so constructedand arranged as to closely approach optimum vapor superheat temperaturesand vapor reheat temperatures, over a wide range of vapor generatingload.

The components of the vapor superheater and the vapor reheater arepreferably arranged in series as to gas flow, and the superheater andthe reheater each involves a section which is predominantlyconvectionally heated, and another section which is predominantly heatedby radiantly transmitted heat, the inherent tendencies of the convectionsections and the radiant sections tending to balance or compensate eachother over a wide range of vapor generating load to approach the optimumreheat and superheat temperatures over the wide load range.

More specifically, the invention involves a vapor generating unit whichhas incorporated therein a high temperature vapor superheater and a hightemperature vapor reheater, both the superheater and the reheater havingwidely spaced platens of tubes disposed in the upper part of avertically elongated secondary furnace chamber which is fired at itslower part at temperatures above the fusion temperatures of the slagforming fuel used in the firing means. A convection gas pass leadslaterally from the upper part of the vertically elongated secondaryfurnace chamber, and within this gas pass there is disposed a convectionheated section of the reheater connected in a series as to vapor fiowwith the radiantly heated section of the reheater. Within the gas passand beyond the convection reheater section there is a bank of tubesconstituting a convection section of the secondary superheater, of whichthe superheater platens at the upper part of the secondary furnacechamber are a part. This bank of tubes within the gas pass is arrangedin series as to vapor flow with the secondary superheater platensdisposed in the upper part of the vertically elongated furnace chamber.Beyond the bank of tubes constituting the convection section of thesecondary superheater is arranged the convection section of a primaryvapor superheater including banks of tubes which extend entirely acrossthe gas flow from one side of the gas pass to the other, without anypartition or division wall disposed within that section of the gas pass.The vaporizable fluid circuit of the unit includes a vapor and liquiddrum in which the generated vapor is separated from the vapor and liquidmixtures entering the drum. The generated vapor passes throughappropriate connections to the convection section of the primarysuperheater, which preferably includes a plurality of banks of tubularsections connected in series as to vapor flow. From the outlet of theconvection section of the primary superheater the superheated vaporflows through an attemperator on its way to the first stage of thesecondary superheater, which includes the widely spaced superheater tubeplatens disposed in the upper part of the secondary furnace chamber.From the outlet of this first stage of the secondary ice superheater thesuperheated vapor flows to the inlet of the second stage of thesecondary superheater, which is formed by the bank of closely spacedconvection heated tubes of a dependent section disposed within the gaspass. From the outlet of that section the superheated vapor flows to thehigh pressure stage of a prime mover. From the exhaust of this highpressure stage the vapor flows to the inlet of the first stage of thereheater which is formed by the widely spaced reheater tube platensdisposed in the upper part of the secondary furnace chamber and betweenthe first stage of the secondary superheater and the remainingsuperheater and reheater sections. From the outlet of this first stageof the reheater, the reheated steam flows to the inlet of a convectionsection of the reheater which is formed by -a bank of closely spacedtubes disposed within the gas pass. From the outlet of this second stageof the 'reheater, the reheated vapor flows to the inlet of a lowerpressure stage of the prime mover.

The invention also includes the method of attaining superheat and reheatcontrol effected by the illustrative unit. The method involves thepassage of the steam to be superheated through a zone which ispredominantly convection heated, and then through a zone which ispredominantly radiantly heated. The method also involves a similarprocedure as to the convection heating and radiant heating of thereheated vapor.

The invention will be concisely set forth in the claims appended hereto,but for a complete understanding of the invention, its uses andadvantages, recourse should be had to the following description whichrefers to a preferred embodiment of the apparatus of the invention, asshown in the accompanying drawings.

In the drawings:

Fig. 1 is a sectional elevation diagrammatically indicating thepertinent features of the illustrative vapor generating, superheating,and reheating unit; and

Fig. 2 is a plan section of the Fig. 1 unit on the line 22 of Fig. 1,and looking in the direction of the arrows.

Fig. 1 of the drawings shows a high capacity vapor generating,superheating and reheating unit including a vertically elongatedsecondary furnace chamber 10. The boundaries of this chamber, such asthe front wall 12 and the rear wall 14, preferably include upright vaporgen erating tubes connectedinto a fluid system including the vapor andliquid drum 16 at the upper part of the unit, and the liquid drum 18 atthe lower part of the unit. Such vapor generating wall tubes areconnected at their upper ends to the drum 16 to discharge vapor andliquid mixtures into the drum for separation of the generated vapor fromthe liquid. In the operation of the unit the inlets of the vaporgenerating tubes are supplied with liquid through the lower drum 18 andone or more large diameter downcorners 20 leading from the liquid spaceof the drum 16 to the lower drum 18.

The vertically elongated secondary furnace chamber 10 is normallysupplied with high temperature gases having temperatures of the range of230.0 F. to 3300 F. by burning slag forming fuel at the lower part ofthe unit, in a cyclone furnace 22, the structure and arrangement ofwhich may be of the nature indicated in the US. patent to Kerr et al.2,594,312 of April 29, 1952. This cyclone furnace normally burns a slagforming fuel such as particle form coal, at temperatures above thefusion temperature of the slag in the fuel. The combustion chamlber 24of the cyclone furnace is supplied withhig-h temperature secondary airin such a manner that cyclonic action of the burning fuel and gasestherefrom is'se't up" within the combustion chamber. The gaseousproducts of combustion flow through the cyclone furnace tliioat 26 intothe primary furnace chamber '28. From primary furnace chamber 28 thecombustion gases with a small percentage of suspended particles thereinpass over the screen formed by the vapor generating tube sections 30 and32 into the lower part of the seconday furnace chamber 10. The upperpart of the secondary furnace chamber, by reason of the dispositiontherein of widely spaced vapor superheater platens and reheater platens,constitutes aradiant vapor heating zone which will be later referred to.

High temperature secondary air for the cyclone furnace 22 is suppliedthrough appropriate ductwork 34 leading from a high temperature airheater (not shown). During the operation of the cyclone furnace moltenslag collecting in the bottom of the combustion chamber 24 flows througha slag opening 36 to the floor 38 of the primary furnace chamber 28, andthence passes into a slag pit 40.

Leading laterally fiom the radiant vapor heating zone at the upper partof the secondary furnace chamber 10 is a convection gas pass in whichthe gases flow substantially horizontally to a turning space 42. Fromthis turning space the gases flow downwardly through the downfiowsection 44 of the convection gas pass, and thence through breeching 46and ductwork 48 leading to a high temperature air heater, and thence toa stack.

Within the vapor and liquid drum 16 there are two rows of cyclone steamseparators 50, each of which is preferably of the type indicated in theUS. patent to Fletcher and Rowand 2,289,970. These devices receive thevapor and liquid mixtures from the vapor generating wall tubes of thesecondary furnace chamber, and discharge the separated vapor into theupper part of the drum. The separated vapor thence proceeds through aseries of conduits 52 along the roof 54 of the unit to the header 56 atthe top of the downflow section of the convection gas pass. Two rows ofsuperheater supply tubes lead from the header 56 downwardly. The tubes'58 of one row lead directly downwardly along the left hand side of thedownflow section of the convection gas pass and thence in spacedrelationship across the lower part of the gas pass as indicated at 60.Their lower ends are connected to the header 62. The tubes 64 of theother row leading from the header 56 lead across the roof of theconvection gas pass as indicated at 66, and thence downwardly along theright hand wall 68 to connection with the header 62. From the header 62rows of tubes 70 lead upwardly to a position beyond the economizer 72where they form the banks 7477 of spaced tubes of the primarysuperheater, thence the outlet portions of these tubes 80 lead directlyupwardly to the out let header 82 of the primary superheater. From theheader 82 the steam flows through one or more conduits 84 to anattemperator which may be of the type indicated in the patent toFletcher et al. 2,550,683 of May 1, 1951. This attemperator operates tocontrol the final steam temperature by the injection of spray water intothe steam in quantities controlled automatically from a plurality ofvariables, the most important one of which may be the final temperatureof the steam. From the attemperator the steam passes through conduits 88and 90 to a secondary superheater inlet header 92' preferably extendingentirely across the width of the unit. From the inlet header 92 and itscompanion outlet header 94 depend a series of widely spaced platens ofsuperheater tubes constituting the first stage of the secondarysuperheater, disposed in a high temperature gas region constituting theradiant vapor superheating and reheating zone. One of these platens isindicated at 96, and the spacing in these platens transversely of theunit is indicated in Fig. 2 of the drawings. The spacing of theseplatens transversely of the unit is preferably 24 inches or more inorder to form this stage of the secondary superheater in such a mannerthat it is predominantly radiantly heated, and in order to promoteoptimum conditions' as to heattran sfenparticularly with respect toslagging conditions and the removal of deposits upon these platens.

From the first and radiant stage of the secondary superheater thesuperheated vapor passes from the outlet header 94 throuh a series ofconduits 98 to the inlet header 100 of the second stage of the secondarysuperheater. This stage is formed by a hank of closely spaced uprighttubular sections 102 pendently arranged within the upper part of theconvection gas pass for transverse flow of the heating gases thereover.This stage of the secondary superheater, because of the gas flowconditions and the close spacing of the component tubes, constitutes asecondary superheater section which is predominantly convection heated.From this second stage of the superheater the superheated vapor passesthrough the outlet tubes 104 to the outlet header 106, and thencethrough one or more conduits 108 to the inlet of a high pressure stage110 of a prime mover. From the exhaust 112 of this prime mover stage thevapor, reduced in pressure, passes through one or more lines 114 to theinlet header 116 of the first stage or radiantly heated section of thereheater. This radiantly heated stage of the reheater is formed by aplurality of pendent platens 118 which are disposed in the upper part ofthe secondary furnace chamber 10, which constitutes the radiant vaporheating zone. These platens are constructed and arranged in a mannersimilar to the construction and arrangement of the platens 96 of thefirst stage of the secondary superheater.

The outlets of the tubes constituting the platens 118 of the first stageof the reheater are connected to the outlet header 120 from whichreheated vapor flows through one or more conduits 122 to the second andpredominantly convection heated stage of the reheater. In this stage ofthe reheater pendently supported and closely spaced tube sectionsconstitute the convection heated banks of tubes 124 and 126.

The side spacing of the tubes of the banks of tubes 124 and 126 of thepredominantly convection heated section of the reheater is much lessthan the spacing of the tubes or the platens in the predominantlyradiantly heated section of the reheater, as indicated particularly inFig. 2 of the drawing. From the outlets of the tubes constituting thepredominantly convection heated stage of the reheater, reheated steampasses to the outlet headers 128 and 130, and thence through conduits132 to the inlet 134 of a lower pressure stage 136 of the prime mover.

The predominantly radiantly heated first stage of the secondarysuperheater has such an inherent heat transfer characteristic that thevapor temperature at the outlet of this section falls below an optimumvalue as the vapor generating load increases, and the predominantlyconvection heated second stage of the superheater has such a heattransfer characteristic that it has an inherent tendency to effectsuperheated vapor temperatures increasing above an optimum value as theload increases. Therefore, the present invention involves suchproportioning of the extent of the surfaces in the predominantlyradiantly heating stage, and the predominantly convection heating stagethat these two opposing tendencies tend to balance each other andtherefore promote the maintenance of a predetermined superheated vaportemperature over a wide range of rate of vapor generation.

Conditions such as those referred to in the immediately precedingparagraph also pertain to the radiantly heated and the convection heatedsections of the reheater. However, the reheater, because of itsconnections with the prime mover, and the different temperatures andpressures of the vapor entering the reheater, with respect to similarconditions of the vapor entering the superheater, the reheater issubject to an additional inherent tendency wherein the reheat effect ofthe convection section of the reheater is such that if the sameproportionate arrangement of surfaces was involved in the combinedreheater as in the superheater, the reheat temperature would tend todepart from a predetermined value when the vapor generating loaddecreases. This invention therefore involves a differentialproportioning of the convection heating surfaces and the radiantlyheated surfaces of the reheater, with respect to the proportioning ofthe Corresponding surfaces of the superheater, for overcoming thisdifferential tendency.

Preferably, aspray attemperator similar to the ratternperator abovereferred to, is incorporated in the reheater circuit.

A temperature control range on both the superheater and the reheater canbe obtained by varying the excess air to the cyclone burner. At controlload the excess air may be increased, from 10% to 30% to obtain fullsteam temperature, and this results in 1.5% spray on the reheater, whichis equivalent to approximately 30 F. safety. If at control load, theexcess air is increased from 30% to 40%, then the superheat temperatureis increased 30 F. (due to the fact it is mostly convection surface),but the reheat temperature only increases F.

With the illustrative superheat and reheat control system, full steamand reheat' temperatures may be controlled from 6Q% to 100% of fullload, and at full load there is only 2% spray water required on thereheater.

For controlling the gas temperature conditions within the secondaryfurnace chamber 10, particularly with respect to maintaining s laggingconditions within an optimum range, and for maintaining the gastemperatures within such a range that they will promote a high degree ofavailability of the unit, from the standpoint of allowable gastemperatures with respect to the metal of the radiantly heated heatedplatens of the secondary superheater land the reheater, the gasesflowing upwardly in the lower part of the secondary furnace chamber mayhave their temperature reduced by mixing therewith lowertemperatureheating gases withdrawn from a pos'ition in the gas flow pathbeyond the economizer 72, and introduced into the lower portion of thesecondary furnace chamber. These results may be effected by a recyclinggas system including a fan 150- having appropriate ductwork 152connecting the inlet of the fan with an opening 154 in the fine orductwork 48 leading from the lower part of the convection gas pass. Theoutlet of the fan 150 is connected by ductwork 156 to a transversedistributing duct 158, from which the lower temperature gases flowthrough the ductwork 160 through a plurality of outlets preferablydistributed across the width of the wall .14 of the secondary furnacechamber. To appropriately form such a series of outlets, alternate vaporgenerating tube's along the secondary furnace chamber wall 14 may bebent out of their wall forming alignment over the vertical extent of theductwork 160.

In the illustrative unit the reheater and thesuperheater components arearranged throughout the full width of the unit, thus reducing the numberof flow circuits. This is not only of importance with respect to theoriginal cost of the unit, by reducing the complexity of themultifarious tubular connections to the various headers employed in anarrangement wherein the superheater and the reheater; components aredivided transversely of the unit. This arrangementof the illustrativeunit is also of particular importance with. respect to the functioningof the reheater. This results from the particularly low pressure drop ofthe illustrative arrangement.

7 Additional vapor generating surface for the Fig. 1 unit is provided bywingWaHs of vapor generating tubes, the lower parts of which aredisposed within the lower part of the secondary furnace chamber 10. Suchtubes lead through the wall 14 of the secondary furnace chamber fromheaders 170 which are appropriately connected into the circulationsystem of the unit. The main parts of these tubes 173 and 174 areclosely spaced and disposed in upright position in the right hand partof the secondary furnace chamber. Just below the arch 176 these tubeshave upwardly inclined or offset portions 178- 480 which lead to otherupright portions, extending in division will formation through that partof the convectional gas pass in which the banks of reheater tubes 124and 126 are disposed. The partition or division walls formed by thesetubes are indicated at 190 and 192 in Fig. 2. At the roof of the gaspass these tubes are bent to be appropriately connected to the vapor andliquid drum 16. They may combine with the upper parts of the rear walltubes 200 to extend to the left at the upper part of the secondaryfurnace chamber, as indicated at 202. Intermediate parts of the rearwall furnace tubes form the lower and upper parts 204 and 206respectively of the arch 176, and the parts of these tubes above thearch extend upwardlyin spaced relation to the superheater supply tubes58 to form a screen extending across the convection gas pass at aposition ahead of the convection stage of the secondary superheater. I

The vapor generating tubes 210 for the front wall of the secondaryfurnace chamber have lower parts bent out of their wall alignment asindicated at 212, so as to form the upper part of the wall dividing theprimary furnace chamber from the lower part of the secondary furnacechamber. Beyond this inclined wall the tubes extend as indicated at 30and 32, and thence to a connection with the drum 18. Others of thesecondary furnace chamber front wall tubes extend along the upright wallof the cyclone furnace as indicated at 214 and 216, and thence along theprimary furnace chamber floor 38 to the header or drum 18. Some of thesetubes are bent to define the throat 26 of the cyclone furnace.

The Fig. 1 unit is preferably rectangular in horizontal cross-sectionand the reheater and superheater headers, as well as the vapor andliquid drum 16 are supported by suitable hangers from rectangularsteelwork, including such beams as the beams 218 supported by columnssuch as 220224 inclusive. The hangers for supporting the drum 16 fromthe beams 218 include a plurality of U- shaped members cradling the drumbetween upwardly extending legs, such as 230 and 232.

The attainment of a constant reheat temperature over a wide range ofvapor generating load is effected in the illustrative unit by takingadvantage of the radiant heat absorption characteristics of the radiantplatens, and proportioning the radiant heating surface to the convectionheating surfaces to supply additional heat absorption reqnired by thereheat vapor, with decreasing load, such additional heat absorptionrequired by the reheater being an increasing function with decreasingload.

The feature of the invention whereby the heat absorption characteristicsof the combination of radiant and convection reheater surface results ina pat-tern of operati-ve results whereby the steam temperatures aremaintained constant over a wide load range, also results in minimizingthe amount of spray water required for attemperation, and maintainingthe spray water requirements substantially constant over a wide loadrange.

The superheater surface of the illustrative unit is so proportionedbetween its first and second stages that the total superheating effectis obtainable by radiant heat absorption and convection absorption, andthrough the use of increased excess air to the cyclone furnace, fulleffect can be obtained on the superheater with a minimum amount ofincrease in excess air.

In the operation of the illustrative unit with recycled gases used forcontrolling the gas conditions within the secondary furnace chamber, gastemperatures entering the convection section may be maintained at a lowvalue and yet the heat absorption to the convection vapor heatingcomponents disposed midway and further downstream in a gas-flow sense inthe convection gas pass, is increased as a result of the increased massflow of gases through the convection section.

the invention is not to be taken as limited to all of the detailsthereof. It is rather to be taken as of a scope commensurate with thescope of the subjoined claims.

What is claimed is:

l. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamber,vapor generating tubes lining the Walls of said furnacechamber, a hightemperature vapor superheater comprising a bank of primary superheatertubes in said gas pass, a bank of pendent secondary superheater tubesarranged in vertical radiantly heated platens widely spaced transverselyof the upper part of said furnace chamber, means for passing vapor to besuperheated through said primary and secondary superheater tube banks inthe order named, a high temperature vapor reheater comprising a bank ofpendent reheater tubes arranged in vertical radiantly heated platenswidely spaced transversely of the upper part of said furnace chamber inthe space between said secondary superheater tube platens and said gaspass, and a bank of pendent vapor reheating tubes arranged in parallelvertical planes across the entire width of said gas pass, and means forpassing vapor to be reheated serially through said reheater tube banksin the order named, said superheater and reheater radiantly heated tubeplatens being formed solely by superheater and reheater tubesrespectively.

2. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamberand having serially connected horizontal and vertical gas flow sectionsconnected by a gas turning space, vapor generating tubes lining thewalls of said furnace chamber, a high temperature vapor superheatercomprising a bank of horizontally extending primary superheater tubes insaid gas pass vertical section, a bank of pendent secondary superheatertubes arranged in vertical radiantly heated platens widely spacedtransversely of the upper part of said furnace chamber, means forpassing vapor to be superheated through said primary and secondarysuperheater tube banks in the order named, a high temperature vaporreheater comprising a bank of pendent reheater tubes arranged invertical radiantly heated platens Widely spaced transversely of theupper part of said furnace chamber and in spaced alignment with saidsecondary superheater tube platens, and a bank of pendent vaporreheating tubes arranged in parallel vertical planes across the entirewidth of the horizontal section of said gas pass, and means for passingvapor to be reheated serially through said reheater tube banks in theorder named, said superheater and reheater radiantly heated tube platensbeing formed solely by superheater and reheater tubes respectively.

3. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamberand having serially connected horizontal and vertical gas flow sectionsconnected by a gas turning space, vapor generating tubes lining thewalls of said furnace chamber, a high temperature vapor superheatercomprising a bank of horizontally extending primary superheater tubes insaid gas pass vertical section, a bank of pendent secondary superheatertubes arranged in vertical radiantly heated platens widely spacedtransversely of the upper part of said furnace chamber, means forpassing vapor to be superheated through said primary and secondarysuperheater tube banks in the order named, a high temperature vaporreheater comprising a bank of pendent reheater tubes arranged invertical radiantly heated platens wide- I ly spaced transversely of theupper part of saidfurnace chamber, and a bank of pendent vapor reheatingtubes arranged in parallel vertical planes across the entire width ofthe horizontal section of said gas pass, means for passing vapor to bereheated through said reheater tube banks in the order named, and bothof said reheater tube banks being'positioned in the space between saidsecondary superheater tube platens and said gas turm g space. a a

4. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burninga'slag-forming fuel in suspension at its lower end, walls defining aconvection heating gas pass opening to one side of the upper end of saidfurnace chamber and having serially connected horizontal and verticalgas flow sections connected by a gas turning space, vapor generatingtubes lining the walls of said furnace chamber, a high temperature vaporsuperheater comprising a bank of horizontally extending primarysuperheater tubes in said gas pass vertical section, a bank ofmulti-looped pendent secondary superheater tubes arranged verticalradiantly heated platens widely spaced transversely of the upper part ofsaid furnace chamber, means for passing vapor to be superheated throughsaid primary and secondary superheater tube banks in the order named, ahigh temperature vapor reheater comprising a bank of pendent reheatertubes arranged in vertical radiantly heated platens widely spacedtransversely of the upper part of said furnace chamber and in spacedalignment with said secondary superheater tube platens, and a bank ofmulti-looped pendent vapor reheating tubes arranged in parallel verticalplanes across the entire width of the horizontal section of said gaspass, means for passing vapor to be reheated through said reheater tubebanks in the order named, and both of said reheater tube banks beingpositioned in the space between said secondary superheater tube platensand said gas turnin space.

5. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, Walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamberand having serially connected horizontal and vertical gas flow sectionsconnected by a gas turning space, vapor generating tubes lining thewalls. of said furnace chamber, a high temperature vapor superheatercomprising a bank of horizontally extending primary superheater tubes insaid gas pass vertical section, a bank of multi-looped pendent secondarysuperheater tubes arranged in vertical radially heated platens Widelyspaced transversely of the upper part of said furnace chamber, a bank ofmulti-looped pendent secondary superheater tubes arranged in closelyspaced vertical parallel .planes across the entire width of the gasturning space of said heating gas pass, means for passing vapor to besuperheated through said primary and plurality ofsecondary superheatertube banks in the order named, and a high temperature vapor reheatercomprising a bank of multilooped pendent vapor reheating tubes arrangedin parallel vertical platens across theentire width of the horizontalsection of said gas pass positioned in the space between said secondarysuperheater tube platens and said bank of secondary superheater tubes insaid gas turning space, said superheater and reheater tube platens beingformed solely by superheater and reheater tubes respectively.

6. A vapor generating, superheatingand-reheating unit comprising wallsdefininga vertically elongated furnace chamber having means for burninga slag-forming fuel in suspension at its lower end, 'walls'definin'g aconvection heating gas pass opening to one sideof the upper end of saidfurnace chamber }and having serially connected horizontal and verticalgas flow sections connected by a gas turning space, vapor generatingtubes lining the walls of said furnace chamber, a high temperature vaporsuperheater comprising a bank of horizontally extending primarysuperheater tubes in said gas pass vertical section, a bank ofmulti-looped pendent secondary superheater tubes arranged in verticalplatens widely spaced transversely of the upper part of said furnacechamber, a bank of multi-looped pendent secondary superheater tubesarranged in closely spaced vertical parallel planes across the entirewidth of the gas turning space of said heating gas pass, means forpassing vapor to be superheated through said primary and secondarysuperheater tube banks in the order named, and a high temperature vaporreheater comprising a bank of pendent reheater tubes arranged invertical platens widely spaced transversely of the upper part of saidfurnace chamber and in spaced alignment with said secondary superheatertube platens, and a bank of multi-looped pendent vapor reheating tubesarranged in parallel vertical planes across the entire width of thehorizontal section of said gas pass, means for passing vapor to bereheated through said reheater tube banks in the order named, and bothof said reheater tube banks being positioned in the space between saidsecondary superheater tube platens and said bank of secondarysuperheater tube platens in said gas turning space.

7. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamber,vapor generating tubes lining the walls of said furnace chamber, a vaporsuperheater comprising a bank of primary superheater tubes in said gaspass, a bank of multi-looped pendent secondary superheater tubesarranged in vertical platens widely spaced transversely of the upperpart of said furnace chamber, a vapor reheater comprising a bank ofmulti-looped pendent vapor reheating tubes arranged in parallel verticalplanes across the entire width of said gas pass, said reheater tube bankbeing positioned in the space between said secondary superheater tubeplatens and said bank of primary superheater tubes, and vapor generatingtubes arranged in a plurality of wing walls having lower portions spacedtransversely of the furnace chamber below the level of said superheatertube platens and upper portions extending vertically through saidgaspass intermediate the width of said reheater tube bank therein.

8. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burningfuel in suspension at its lower end, walls defining a convection heatinggas pass opening to one side of the upper end of said furnace chamber,vapor generating tubes lining the walls of said furnace chamber, a hightemperature vapor superheater comprising a bank of horizontallyextending primary superheater tubes in said gas pass, a bank of pendentsecondary superheater tubes arranged in vertical platens widely spacedtransversely of the upper part of said furnace chamber, a hightemperature vapor reheater comprising a bank of pendent reheater tubesarranged in vertical platens widely spaced transversely of the upperpart of said furnace chamber, and a bank of pendent vapor reheatingtubes arranged in parallel vertical planes across the entire width ofsaid gas pass, and both of said reheater tube banks being positioned inthe space between said secondary superheater tube platens and said bankof primary superheater tubes, and vapor generating tubes arranged in aplurality of wing walls having lower portions spaced transversely of thefurnace chamber below the level of said superheater and reheater tubeplatens and upper portions extending vertically through said gas passintermediate the width of said reheater tube bank therein.

9. A vapor generating, superheating and reheating unit comprising wallsdefining a vertically elongated furnace chamber having means for burninga slag-forming fuel in suspension at its lower end, walls defining aconvection heating gas pass opening to one side of the upper end of saidfurnace chamber and having serially connected horizontal and verticalgas flow sections connected by a gas turning space, vapor generatingtubes lining the walls of said furnace chamber, a high temperature vaporsuperheater comprising a bank of horizontally extending primarysuperheater tubes in said gas pass vertical section, a bank ofmulti-looped pendent secondary superheater tubes arranged in verticalplatens widely spaced transversely of the upper part of said furnacechamber, a. bank of multi-looped pendent secondary superheater tubesarranged in closely spaced vertical parallel planes across the entirewidth of the gas turning space of said heating gas pass, means forpassing vapor to be superheated through said primary and secondarysuperheater tube banks in the order named, a high temperature vaporreheater comprising a bank of pendent reheater tubes arranged invertical platens widely spaced transversely of the upper part of saidfurnace chamber and in spaced alignment with said secondary superheatertube platens, and a bank of multi-looped pendent vapor reheating tubesarranged in parallel vertical planes across the entire width of thehorizontal section of said gas pass, means for passing vapor to bereheated through said reheater tube banks in the order named, and bothof said reheater tube banks being positioned in the space between saidsecandary superheater tube platens and said bank of secondarysuperheater tube platens in said gas turning space, and vapor generatingtubes arranged in a plurality of wing walls having lower portions spacedtransversely of the furnace chamber below the level of said superheaterand reheater tube platens and upper portions extending verticallythrough said gas pass horizontal section intermediate the width of saidreheater tube bank therein.

References Cited in the file of this patent UNITED STATES PATENTS2,685,279 Caracristi Aug. 3, 1954 2,737,930 Rowand et a1. Mar. 13, 1956FOREIGN PATENTS 1,046,913 France July 15, 1953

